Bimetal thermostat



March 5, 1935. H. sco'rT 1,993,020

BIMETAL THERMOSTAT Filed May 11, 1934 WITNESSES INVENTOR Howard S0027.

' AZI'TORNE Patented Mar. 5, 1935 UNITED S'lATES PATENT OFFICE inghouseElectric a Manufacturing Company, East Pittsburgh, l'a., a corporationof Pennsylvauia Application May 11, 1934, semi No. 125,116

4Ciaims.

My invention relates to temperature-responsive devicesand moreparticularly to bimetal thermostats. v

It is an object of my invention to provide a I bimetal thermostat whichwill have optimum operating characteristics not only as to deflectionunder changes of temperature, but also as to the maximum temperature towhich the device can be safely subjected.

Anotherobiectof my invention is to provide a bimetal element that shallhave good manufacturing characteristics, that is, one which may beeasily cold rolled to size without acquiring appreciable curvature,twist or excessive distortion 16 from a plane surface at roomtemperature.

In practicing my invention I provide more particularb two iron-alloyswhich may be welded or otherwise united with each other, the elementhaving the high temperature coeilicient of ex- 20 pansion containingfrom 26% to 7% of nickel, from 2% to 6% of manganese, from 1/10% to 10%of chromium and from .05% to .25% of carbon with traces of cobalt. Thelow expansion component is an iron alloy including from 35% 25 to 12% ofnickel, from .10% to 35% of cobalt,

from .10% to 1.0% manganese, from .10% to 8% of chromium, molybdenum,tungsten or titanium eithensingle or in combination and from .05% to.25% of carbon.

30 The single figure of the drawing illustrates one form of device whichmay embody the invention, namely, a bimetal strip 11 havinga-hi'gh-expansion component 13 and a low-expansion component 15.

In my earlier Patent 1,671,490 I have disclosed and claimed ahigh-expansion component including 10% of nickel and 10% of manganese incombination-with iron and-other metals in minor quantities. I havefound, as the result of I 40 further development work on,.bimetals ofthis general composition that a 10% nickel, 10% manganese iron alloy hasrather a poor resistance to corrosion, as well as somewhatunsatisfactory rolling characteristics. I have found that the corrosionresistance is materially improved by an increase in the amount of nickelin the high-expansion component with an accompanying reduction in theamount of manganese present in the alloy.

I have also found that an alloy of the abovedescribed generalcomposition has somewhat objectionable cold rolling characteristics inthat the bimetal takes on a cross curvature or other permanentdistortion because of the fact that the 5 high expansion alloy is harderthan the low-expansion alloy usually associated therewith, and alsobecause the high-expansion alloy hardens more rapidly when being coldrolled. This disadvantage may be partially corrected without impairingthe resistance to corrosion by substituting chromium for part of eitherthe nickel or the manganese in the high-expansion alloy.

As a result of numerous experimental compositions and tests on the sameI have found that the composition is governed quite closely by thefollowing:

%nickel+2.5(%manganese) 2( %chromlum) +l8(%carbon) (Equation 1) shouldbe between 32 to 36, while at the same time, the carbon content .isappreciably less than .3% and preferably is .l%, the nickel content isless than 26% and above 7%, the chromium is of %.nickel, 6% manganese,4% chromium,

.l% carbon, the remainder being iron and incldental elements normal insteel. These alloys are non-magnetic.

I prefer to combine such a high-expansion component with a low-expansionalloy contaih- Another ing nickel or nickel and cobalt, with thecombined nickel and cobalt content ly xbetween 34% and 55%, the majorportion of the alloy being iron. Chromium, molybdenum-tungsten ortitanium, either singly or in combination may be substituted for a partof the nickel content in order to obtain better working qualities andgreater strength of the alloy at high temperatures. Although chromium issomewhat detrimental to the expansion properties of the low expansioncomponent, its effect may be neutralized, at least in part, by anincrease in the cobalt content by the amount that the nickel content isdecreased when chromium, molybdenum,

tungsten or titanium or combinations thereof are added. v

I have found that the relation between the amount of chromium or itsequivalents and nickel in the low expansion alloy may be set forth inthe following equation:

% Fe .50 to .60

(Equation 2) A concurrent requirement is that, as stated above, thepercentage of the nickel plus cobalt should be between 34% and 55%.

Table I gives a number of different compositions of ahigh-expansioncomponent, these compositions meeting the requirements set-forth abovein Equation 1.

Table I.-Hiah-expanston component Ni 0 M y o 7 o H o n r approxa 0 mum 120 Traces 2 o 1 0.1 71.8 2 Z; Traces 3 1 .1 72.9 a 20 Traces 2 4 .1 70.04 11s Traces 4 4 .1 10.0 5 1o Traces o 4 .1 10.0 6 7 Traces 6 5 1 81.9

Table 11 gives a number of compositions of a low-expansion componentmeeting the requirement of Equation 2 given above.

Table IILow-e:cpansion component Mo, W, T1 or e Ni C0 Mn 01' 0(approximately) 1 a5. 0.1 o. 1 0.1 0.1 64. 0 2 31.9 4.1 .5 .1 .1 63.3 320. 12.0 .5 2.0 .1 50.0 4 18.0 2?. 0 .5 s. o 1 54. o 5 28.6 13.4 .s .1.1 57.3 0 2s. 0 20. 0 s 2. 0 1 54 o 7 17.0 as. 0 s 4 o 1 so. 0 s 12.034. 0 .5 0.0 .1 41.0

It may be noted that compositions 1 to 4, inclusive, in Table II willcooperate with any one of the alloys in Table I to give a maximumdeilection of a bimetal element including them, at temperatures betweenzero to C. while alloys 5 to 8, inclusive, of Table II when combinedwith any one ofthe high-expansion components in Table I will have amaximum deflection over a temperature range of C. to 300 C. or even 400C.

Various modifications may be made in the device embodying my inventionwithout departing from the spirit and scope thereof, and I desire,therefore, that only such limitations shall be placed thereon as areimposed by the prior art or are set forth in the appended claims.

I claim as my invention:

1. A thermostatic element comprising a pair of cooperating metallicmembers having diiferent temperature coeflicients of expansion, the highexpansion member being an iron-nickel alloy including lesser quantitiesof manganese, chromium and carbon, the relation between the percentagesof nickel, manganese, chromium and carbon being expressed by the formulathe value of which should lie between 32 and 36, the nickel content tobe between 7% and 26%, the chromium content to be between 10% and .1%and the carbon content to be between .05% and 3%, and the low expansionmember being an iron-nickel-cobalt-chromium alloy including minorquantities of manganese and carbon, the relation between the percentagesof iron, nickel, manganese, chromium and carbon being expressed by theformula the value of which should lie between .50 and .60

the combined percentage of nickel and cobalt be ing between 34 and 55.

2. A thermostatic element comprising a pair of cooperating metallicmembers having different temperature coeflicients of expansion, the highexpansion member being non-magnetic and having substantially thefollowing composition,

Per cent. Nickel 26. to '7. Manganese 2. to 8. Chr 0.1 to 5. CobaltTraces Carbon 0.1 Iron and impurities Remainder and the low expansionmember having substantially the following composition,

Per cent. Nickel 35. to 12.0 Manganese 0.1 to 1.0 Chromium, tungsten,molybdenum or titanium 0.1 to 8.0 Cobalt 0.1 to 35.0 Carbon 0.05 to 0.25Iron and impurities Remainder 3. A thermostatic element comprising apair of cooperating metallic members having different temperaturecoefficients of expansion, the high expansion member havingsubstantially the following composition,

Per cent. NickeL Manganese 2. Chromium 4 Carbon 0.1 Cobal Traces Ironand impurities-.. Remainder and the low expansion member havingsubstantially the following composition,

Per cent. Nickel 26.0 Cobalt 12.0 Chromium, tungsten, molybdenum.

titanium 2.0 Manganese .5 Carbon .1 Iron and impurities Remainder 4. Athermostatic element comprising a pair of cooperating metallic membershaving different temperature coefiicients of expansion, the highexpansion member having substantially the following composition,

Per cent. Nickel Manganese 6. Chromium 5. Carbon .1 Co Traces Iron andimpurities Remainder and the low expansion member having substan- HOWARDSCOTT.

